Activation of the tumor suppressor p53 is critical for avoiding carcinogenesis. This activation is based partly on an increase in the cellular levels of p53 protein. Also critical for activating p53 function in response to genotoxic insults is the addition of specific post- translational modifications on p53. Over the past 15 years, a great deal of effort has been devoted to deciphering how individual modifications control p53 activity. We have recently identified a previously unknown modification, the acetylation of lysine residue 357. This residue lies adjacent to an essential structural domain of p53, the oligomerization domain. However, it remains unknown whether K357 acetylation plays a role in this or some other aspect of p53 function. Furthermore, we know little of the enzymes responsible for adding and removing K357 acetylation. While our data clearly demonstrate that K357 acetylation occurs rapidly after DNA damage, we have been unable to implicate K357 acetylation in the classical cell cycle arrest or apoptosis activities of p53. Instead, our preliminary studies suggest a role for K357 acetylation in a less well-understood aspect of p53 function, the induction of cellular senescence. Furthermore, it appears that K357 acetylation may be reversed by the resveratrol-activated sirtuin family of enzymes. These enzymes have been implicated in aging, presenting the attractive model that their control of K357 acetylation levels may contribute to their ability to regulate cellular senescence and aging. Here we outline an experimental plan that will provide an important knowledge base about the enzymology of K357 acetylation and about its functional consequences. These exploratory studies span in vitro biochemical analysis and in vivo tumor suppression assays. Cumulatively, the successful completion of these Aims should provide us with critical knowledge about the novel p53 acetylation event we have defined. This knowledge base will allow for more long-term studies that might ultimately exploit this pathway in the clinic. PUBLIC HEALTH RELEVANCE: The tumor suppressor p53 is the most commonly mutated gene in human cancer and understanding how it helps protect cells from malignant transformation is a central goal of cancer research. We have identified a new regulatory event, the acetylation of a critical domain of p53, that likely participates in controlling its function. Understanding the role of this acetylation event may lead to new diagnostics in cancer and potentially novel therapeutic strategies in the overwhelming percentage of patients whose tumors harbor lesions in the p53 pathway.